Conventionally, as a heat transfer tube through which a heating medium such as water flows, a tube with an inner surface fin equipped with a fin for forming multi-screws on an inner surface has been known (for example, see Japanese Patent Publication No. 5-118507). The interior of the tube with the inner surface fin has a subcritical pressure. In some cases, water flowing through the interior of the tube with the inner surface fin having the subcritical pressure is subjected to film boiling by heating the heat transfer tube. When the film boiling occurs, since the heat transfer decreases by a steam film formed on the inner surface of the tube, the temperature of the tube increases. Therefore, in the tube with the inner surface fin, the fin has a predetermined shape so as to suppress the temperature rise of the tube due to the film boiling. Specifically, the tube with the inner surface fin is configured so that a lead of the fin is 0.9 times a square root of an average tube inner diameter at a maximum level or a radial height of the fin is 0.04 times the average tube inner diameter at a minimum level.
Furthermore, as a heat transfer tube used in a once-through type steam generator of a supercritical pressure variable pressure operation type, a water-wall tube (rifled tube) of a water-cooled tube wall group has been known (for example, see Japanese Patent Publication No. 6-137501). The rifled tube is provided with a spiral projection on its inner surface. The once-through type steam generator performs a subcritical pressure operation in a partial load operation, and by providing the spiral projection on the inner surface of the rifled tube, the tube wall temperature of the rifled tube is kept below an allowable temperature at the time of subcritical pressure operation.